LECTURE 5: PHASE EQUILIBRIA. PHASE EQUILIBRIA. Phase equilibrium describes the way phases (such as solid, liquid and/or gas) co-exist at some temperatures and pressure, but interchange at others. Energetic introduction to phase equilibria. Why does an ice cube melt in the mouth?.
Phase equilibrium describes the way phases (such as solid, liquid and/or gas) co-exist at some temperatures and pressure, but interchange at others.
Why does an ice cube melt in the mouth?
A phaseis a component
within a system,
existing in a precisely
defined physical state,
e.g. gas, liquid, or a
solid that has a single
Concerning transitions between the two phases ‘1’ and ‘2’, Hess’s Law states that H(1→2) = −1 ×
A phase diagram is a graph showing values of applied pressure and temperature at which equilibrium exists.
A phase boundary is a line on a phase diagram representing values of applied pressure and temperature at which equilibrium exists.
The triple point on a phase diagram represents the value of
pressure and temperature at which three phases coexist at equilibrium.
Why does water placed in the freezer become ice?
the tin allotropes have very
different densities ρ, so ρ(tin, grey) = 5.8 gcm−3 but ρ(tin, white) = 7.3 gcm−3.
Phase transitions involving liquids and gases are generally fast!
How is the ‘Smoke’ in horror films made?
The effect of temperature on phase change: sublimation
How does freeze drying work?
Freeze-drying is a layman’s description, and acknowledges that external conditions may alter the conditions of a phase change, i.e. the drying process (removal of water) occurs at a
temperature lower than 100 ◦C.
HOW DOES A ROTARY EVAPORATOR WORKS?
How is coffee decaffeinated?
The intensive properties
of the liquid
and gas (density, heat
capacity, etc.) become
equal at the critical
point, which is
the highest temperature
and pressure at
which both the liquid
and gaseous phases
of a given compound
Why is ice so slippery?
The effect of p and T on the position of solid liquid equilibrium
Consider a car weighing 1000 kg (about 2200 lbs) parked on a sheet of ice at 273.15 K. Take the area under wheels in contact with the ice as 100 cm2 i.e. 10−2 m2. What is the new melting temperature of the ice – call it T(final)? Take H O(melt) = 6.0 kJmol−1 and water Vm(melt) = −1.6 × 10−6 m3 mol−1.
Paraffin wax has a normal melting temperature
T(melt) of 320 K. The temperature of equilibrium is raised
by 1.2 K if the pressure is increased fivefold. Calculate Vm for the wax as
it melts. Take H(melt) = 8.064 kJ mol−1.
How many components are present in a system in which ammonium chloride undergoes thermal decomposition?
The reaction is:
NH4Cl(s) NH3(g) + HCl(g)
C = 2, so F = 4 – P.
A mixture of 50 g of hexane (0.59 mol C6H14) and 50 g of nitrobenzene (0.41 molC6H5NO2) was prepared at 290 K. What are the compositions of the phases, and in what proportions do they occur? To what temperature must the sample be heated in order to obtain a single phase?